The permeability of electrotonic junctions as a function of developmental characteristics will be studied in embryonic tissues. The role of the CNS in the development and dissolution of gap junctions between differentiating muscle cells in amphibian embryos will also be examined. Utilizing the changing developmental features of the amphibian Mauthner cell attempts will be made to specify the factors regulating dendritic differentiation and synaptic input location. Studies of mouse spinal ganglia-spinal cord interactions in vitro will employ morphological labelling techniques to examine mechanisms of medullary and spinal target cell location by dorsal root afferents. Development of abnormal membrane structure and function of neurons in feline GMl-gangliosidosis will be studied. Morphophysiological studies of neuronal interaction will employ the Mauthner fiber-giant fiber synapse of the hatchetfish and frog neuromuscular junctions to analyze the comparative neurobiology of synaptic vesicle-transmitter release relations. Electroreceptors will provide the basis for an investigation into the operation of secondary receptors and their transmitter release mechanisms. The morphological features of rectifying electrotonic junctions will be studied with freeze-fracture techniques. Feeding behavior in the opistobranch, Navanax will be analyzed at the cellular level of synaptic organization. The neuronal subsystems involved in eye movement control in mammals and the functional sign of basal ganglia and cerebellum inputs to thalamus will also be explored.